Science: Periodic Table — Groups, Properties, and Trends

The modern periodic table has 118 elements arranged in 7 periods (rows) and 18 groups (columns). Kerala PSC frequently asks about group properties, periodic trends, and specific element facts. This note covers all essential details.

Structure of Periodic Table

Feature	Detail
Total elements	118 (as of 2016; last 4 added: Nihonium, Moscovium, Tennessine, Oganesson)
Periods (rows)	7
Groups (columns)	18
s-block	Groups 1-2 (+ He)
p-block	Groups 13-18
d-block	Groups 3-12 (transition metals)
f-block	Lanthanides + Actinides (placed below main table)

Group 1: Alkali Metals

Element	Symbol	Atomic No.	Key Property
Lithium	Li	3	Lightest metal; used in batteries
Sodium	Na	11	Common salt (NaCl); highly reactive
Potassium	K	19	Essential for nerve function; banana rich
Rubidium	Rb	37	Used in atomic clocks
Caesium	Cs	55	Most electropositive element; used in atomic clocks
Francium	Fr	87	Most reactive metal; radioactive; rarest

Property	Trend (top to bottom)
Reactivity	Increases (Cs most reactive)
Melting point	Decreases
Density	Generally increases
Atomic radius	Increases
Ionization energy	Decreases
Stored in	Kerosene (to prevent reaction with air/water)

Key Facts:

• All react vigorously with water producing H2 gas + alkali (MOH)
• All have +1 oxidation state
• Soft metals — can be cut with knife
• Flame colours: Li = crimson, Na = golden yellow, K = violet

Group 2: Alkaline Earth Metals

Element	Symbol	Atomic No.	Key Property
Beryllium	Be	4	Toxic; used in X-ray windows
Magnesium	Mg	12	Burns with brilliant white flame; chlorophyll
Calcium	Ca	20	Bones, teeth, cement, limestone
Strontium	Sr	38	Crimson flame; fireworks
Barium	Ba	56	Barium meal for X-ray imaging
Radium	Ra	88	Radioactive; discovered by Marie Curie

Property	Detail
Oxidation state	+2
Harder than	Group 1 metals
Reactivity	Less than Group 1 but increases down the group
Flame: Ca	Brick red
Flame: Ba	Apple green

Group 17: Halogens (“Salt-formers”)

Element	Symbol	State at RT	Color	Key Fact
Fluorine	F	Gas	Pale yellow	Most electronegative element; strongest oxidizer
Chlorine	Cl	Gas	Greenish yellow	Water purification; bleach
Bromine	Br	Liquid	Reddish brown	Only non-metal liquid at room temperature
Iodine	I	Solid	Purple/violet	Thyroid function; antiseptic (tincture)
Astatine	At	Solid	—	Radioactive; rarest naturally occurring element

Property	Trend (top to bottom)
Reactivity	Decreases (F most reactive non-metal)
Electronegativity	Decreases
Melting/Boiling point	Increases
Atomic radius	Increases
Color intensity	Darkens
Oxidation states	F = -1 only; others = -1, +1, +3, +5, +7

Group 18: Noble Gases (Inert Gases)

Element	Symbol	Atomic No.	Key Use
Helium	He	2	Airships, balloons, diving tanks (with O2), cryogenics
Neon	Ne	10	Neon signs (reddish-orange glow), advertising
Argon	Ar	18	Welding shield gas; electric bulbs (most abundant noble gas)
Krypton	Kr	36	Flash photography; some fluorescent lights
Xenon	Xe	54	Headlights; first noble gas compound (XeF2) by Bartlett (1962)
Radon	Rn	86	Radioactive; health hazard in basements

Property	Detail
Valence electrons	Fully filled outer shell (stable octet, He = duplet)
Reactivity	Extremely low (hence “noble” / “inert”)
Bonding	Generally no bonds (Xe forms some compounds)
Physical state	All gases at room temperature
Odor/color	All colorless and odorless

Transition Metals (d-block: Groups 3-12)

First Row Transition Metals (Period 4)

Element	Symbol	Atomic No.	Key Property/Use
Scandium	Sc	21	Lightweight alloys; stadium lights
Titanium	Ti	22	Strong, lightweight; aircraft, implants
Vanadium	V	23	Steel hardening; vanadium steel
Chromium	Cr	24	Stainless steel; chrome plating; shiny
Manganese	Mn	25	Steel making; dry cell batteries (MnO2)
Iron	Fe	26	Most used metal; hemoglobin; steel
Cobalt	Co	27	Blue color pigment; Vitamin B12
Nickel	Ni	28	Coins; stainless steel; electroplating
Copper	Cu	29	Electrical wiring; coins; brass/bronze
Zinc	Zn	30	Galvanization; brass; immune function

Properties of Transition Metals

Property	Detail
Variable oxidation states	Multiple states (e.g., Fe = +2, +3; Mn = +2 to +7)
Colored compounds	Due to d-d electron transitions
Catalytic activity	Many are catalysts (Fe in Haber process, V2O5 in Contact process)
Form complex ions	[Cu(NH3)4]2+ (deep blue), etc.
High melting points	Generally very high (W = 3422 degrees C — highest of all metals)
Good conductors	Heat and electricity
Magnetic properties	Fe, Co, Ni are ferromagnetic
Form alloys	Steel, brass, bronze, stainless steel

Periodic Trends (Left to Right across Period)

Property	Trend	Reason
Atomic radius	Decreases	More protons pull electrons closer
Ionization energy	Increases	Harder to remove tightly held electron
Electronegativity	Increases	Greater attraction for bonding electrons
Metallic character	Decreases	Metals on left, non-metals on right
Electron affinity	Generally increases	More tendency to gain electron

Periodic Trends (Top to Bottom in Group)

Property	Trend	Reason
Atomic radius	Increases	New shells added
Ionization energy	Decreases	Outer electron farther from nucleus
Electronegativity	Decreases	Less attraction for electrons
Metallic character	Increases	Easier to lose electrons
Reactivity (metals)	Increases	Easier to lose valence electron
Reactivity (non-metals)	Decreases	Harder to gain electron

Important Elements — Special Facts

Fact	Element
Most abundant in universe	Hydrogen
Most abundant in Earth’s crust	Oxygen (46.6%)
Most abundant metal in Earth’s crust	Aluminium (8.1%)
Hardest natural substance	Diamond (carbon allotrope)
Highest melting point (metal)	Tungsten (W) — 3422 degrees C
Highest melting point (non-metal)	Carbon (graphite sublimes at 3642 degrees C)
Lightest element	Hydrogen
Lightest metal	Lithium
Heaviest naturally occurring	Uranium (U-238)
Most electronegative	Fluorine (3.98 on Pauling scale)
Most electropositive	Caesium
Liquid metals at RT	Mercury (Hg) and Gallium (Ga near RT, mp 29.76 degrees)
Liquid non-metal at RT	Bromine
Best conductor of electricity	Silver (then Copper, Gold)

Allotropes (Same Element, Different Forms)

Element	Allotropes
Carbon	Diamond, Graphite, Fullerene (C60), Graphene, Carbon nanotubes
Oxygen	O2 (oxygen), O3 (ozone)
Phosphorus	White, Red, Black phosphorus
Sulphur	Rhombic, Monoclinic sulphur
Tin	White tin, Grey tin

PSC Frequently Asked Questions

Question	Answer
Father of Periodic Table	Dmitri Mendeleev (1869)
Modern Periodic Law based on	Atomic number (Henry Moseley, 1913)
Mendeleev’s law based on	Atomic mass
Most reactive metal	Caesium (or Francium, but Fr is extremely rare)
Most reactive non-metal	Fluorine
Noble gas used in balloons	Helium (not Hydrogen — safety)
Element in pencil lead	Carbon (graphite)
Element in thermometer	Mercury
Rust is	Iron oxide (Fe2O3.xH2O)
Brass =	Copper + Zinc
Bronze =	Copper + Tin
Stainless steel =	Iron + Chromium + Nickel + Carbon
German silver (no silver) =	Copper + Zinc + Nickel

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Memory Aid: Periodic trends across a period: “RAID” — Radius decreases, Affinity increases, Ionization energy increases, electronegativity increases (all going left to right).